1. Field of the Invention
The present invention relates to a module having a Peltier element.
The Peltier element is thermally coupled with an element having a temperature response and is used to keep the element at a fixed temperature and stabilize the operation thereof. For example, the Peltier element is thermally coupled with a semiconductor laser diode, which is thus capable of emitting a constant light output irrespective of temperature variations. Generally, an element having a temperature response and a Peltier element are formed in a module formation in which the above elements are accommodated in a package.
2. Description of the Related Art
FIG. 1 is a cross-sectional view of a conventional laser diode module, which has a package 10 made of an insulating member such as a ceramic member. A Peltier element 14 is fixed to the package 10 through a soldering layer 12 A carrier 16 is soldered to the top of the Peltier element 14. A laser diode 18 is fixed to the top of the Peltier element 14 by soldering of the like. A plurality of pads 20 and 22 for wire bonding are provided on the carrier 16. Terminals of the laser diode 18 are electrically connected to the pads 20 and 22 by bonding wires 24 and 28. The pads 20 and 22 are electrically connected to external connection terminals (not shown) supported by the package 10 by bonding wires 26 and 30, which are also grounded.
FIG. 2 is an equivalent circuit of the laser diode module shown in FIG. 1. An inductance component L1 of the bonding wires 28 and 30 is connected to a cathode of the laser diode 18, and an inductance component L2 of the bonding wires 24 and 26 is connected to an anode thereof. A capacitance C of the Peltier element 14 is present between the anode of the laser diode 18 and the ground. The laser diode 18 is directly or indirectly modulated in accordance with data to be transmitted.
However, the conventional module having the Peltier element shown in FIG. 1 has problems due to the presence of the capacitance C of the Peltier element 14. More particularly, a series resonance circuit is formed by the capacitance C of the Peltier element 14 and the inductance L1 of the bonding wires 24 and 26, and affects the frequency response of the laser diode 18. For example, as shown in FIG. 3, a resonance point exists in the usable frequency band of the laser diode 18, and deteriorate the waveform of a driving signal applied to the laser diode 18. For example, the driving signal may have an overshoot or undershoot portion. Hence, a light signal emitted by the laser diode 18 is deformed, so that the optical transmission characteristic will be degraded.